1. Field of the Invention.
The field of the invention is puncturing devices for insertion into the body. More particularly, the field of the invention is such devices which are inserted into the body under the guidance of an ultrasound visualization system.
2. Brief Description of the Prior Art.
It is known in the prior art to insert a puncturing cannula into the body under the guidance of an ultrasound visualization system aimed at the area of puncture. U.S. Pat. No. 3,556,079 to Omizo and U.S. Pat. No. 4,029,084 to Soldner are two patents relating to ultrasonically guided puncturing cannula apparatus.
Under certain circumstances however, the needle can not be directly viewed by the ultrasound visualization system. For instance, at the point of entry into the body the puncturing cannula is typically not within the scanning region of the ultrasound system. U.S. Pat. No. 4,058,114 to Soldner discloses an ultrasound puncturing guidance system which utilizes an aiming pin, superimposed over the viewing screen, to aid in the aiming and locating of the puncturing needle. U.S. Pat. No. 4,058,114 also discloses the use of a displacement scale system in which the needle position and distance calibration are indirectly determined by referring to displacement markings on the aiming pin.
The needle is sometimes not visible on the viewing screen even when it is within the scanning region. This is because the difference in the reflective properties of the needle and the surrounding tissue is sometimes not sufficient enough to make the needle distinguishable. The tendency of the needle to disappear on the viewing screen is accentuated at sharper angles of insertion into the body (approaching 90.degree. with respect to the body surface--depending on the area being probed, the needle may become difficult to detect at an angle of incidence of as little as 45.degree. or less). The needle may also disappear from the viewing screen if it bends slightly away from the scanning plane during the insertion process.